1. Field of the Invention
This invention relates to methods and compositions, especially those comprising retinoids, preferably topically applied, which are useful for improving keratinocyte and fibroblast proliferation, decreasing matrix metalloproteinase (MMP) expression, and improving collagen synthesis in elderly skin, thus providing as an effect the rejuvenation of aged skin.
2. The State of the Art
As far as mammals go, humans are essentially hairless; that is, most of the skin of the human body can be seen without interference from hair. The skin is thus exposed to whatever insults (natural and man-made) the environment harbors. Since it was first understood that the sun caused erythema, people have taken measures to avoid its xe2x80x9charmful rays.xe2x80x9d A century ago, in Elizabethan England, it was the fashion to avoid the sun at all costs. Yet the skin of those Elizabethans still wrinkled and displayed other signs of chronological aging.
Human skin is a complex organ which extends over the entire body. There are different types of skin at different portions of the body; for example, facial skin is different from that of the scalp, and even the skin on the front (palm) of the hand is different than that on the back of the hand. Although the type of skin can vary over a person""s body, skin is generally composed of two main layers of tissue. The epidermis or cuticle, the outermost layer, is composed of superficial layers (from the outside in: stratum corneum, stratum lucidem, and stratum granulosum) and deep layers (stratum spinosum and stratum basale). The dermis, cutis vera, or the true skin, is composed of a papillary layer above and a reticular layer below.
Since ancient times, a variety of substances have been applied to the skin to improve its appearance, generally by affecting the outermost layer of the skin, or to treat a skin ailment, generally by affecting the true skin. More recently, efforts have been made to rejuvenate the skin and reclaim the elasticity and suppleness lost from exposure to sunlight (UV radiation) and weather.
There is a difference between the physiology of chronologically-aged or intrinsically-aged skin (old skin) in comparison with that of photoaged skin (i.e., skin that appears old due to damage from solar UV irradiation). Old skin typically maintains a smooth and unblemished appearance, in comparison with the leathery, blotchy, and often deep wrinkling of photoaged skin. The epidermis of old skin is typically thinner than normal, whereas that of photoaged aged skin is typically thicker than normal (acanthotic) and atrophies over time. Photoaged skin typically has a large Grenz zone (a wide band of eosinophilic material just beneath the epidermis, and collagen formation and structures indicative of wound healing) which is absent from chronologically-aged skin. See also N. A. Fenske and C. W. Lober, xe2x80x9cStructural and functional changes of normal aging skin,xe2x80x9d J. Am. Acad. Dermatol., 15:571-585 (1986).
Kligman et al., in EP-A2-0 379,367 describe a method for the treatment or prevention of intrinsically aged skin with retinoids. Kligman et al. tested all trans-retinoic acid (as Retin-A(copyright) cream) on albino hairless mice and on 5 elderly Caucasian women; only clinical observations were made of the women before and after the study, and only one biopsy was reported taken and this occurred six months into the treatment (i.e., there is no disclosure in this publication of a reference biopsy taken from the biopsied subject before treatment or from an early period of treatment).
U.S. Pat. Nos. 3,932,665 and 4,934,114 disclose the use of retinal (Vitamin A aldehyde), for the treatment of acne and for the treatment of skin keratoses, respectively; see also U.S. Pat. No. 3,060,229. Retinal and it derivatives have also been suggested as useful in the treatment of such conditions as wrinkles, warts, psoriasis, eczema, dandruff, and the like (see EP-A2-0 391 033). There is also evidence to indicate that tretinoin (all trans retinoic acid) improves the appearance of photoaged skin. Albert M. Kligman, xe2x80x9cCurrent Status of Topical Tretinoin in the Treatment of Photoaged Skin,xe2x80x9d Drugs and Aging, 2 (1):7-13 (1992); and Chas. N. Ellis et al., xe2x80x9cTretinoin: Its Use in Repair of Photodamage,xe2x80x9d and A. S. Zelickson et al., xe2x80x9cTopical Tretinoin in Photoaging: An Ultrastructural Study,xe2x80x9d both in Journal of Cutaneous Aging and Cosmetic Dermatology, Vol. 1, No. 1, p. 33-40 and 41-47 (1988).
Burger et al., in U.S. Pat. No. 5,665,367, describes compositions for topical application to the skin that contain naringenin and/or quercetin, and a retinoid. The compositions are described as useful for treating many unrelated skin conditions, such as wrinkles, acne, skin lightening, and age spots. The action of their composition on human skin is described with respect to an enzyme (transglutaminase) important to the formation of the cell envelope and thus to the epidermis. In contrast, the present invention is directed to changes in the dermis and the proliferation of beneficial dermal cells and structures.
The primary invention is the discovery of a method for rejuvenating human skin. As used with respect to the description and claiming of this invention, xe2x80x9crejuvenatingxe2x80x9d includes the steps of simultaneously preventing collagen degradation and stimulating the formation of new collagen in aged human skin. The invention is based on biopsies of treated and untreated sun-protected human skin from aged (80+ year old) volunteers compared with biopsies of sun-protected skin from younger individuals. In comparison with the skin from younger people, aged skin is thinner, has fewer cells in the epidermis (keratinocytes) and dermis (fibroblasts), has less dense and more disorganized connective tissue, has higher levels of cJun kinase activity and matrix metalloproteinases (MMPs), and has reduced levels of ERK activity, cyclin D2, and Types I and III procollagen.
In summary, we have found as one invention that aged human skin can be rejuvenated by the topical administration of one or more compounds in amounts effective to inhibit collagen degradation and to promote procollagen synthesis, the application preferably being performed on a regular basis. A preferred class of compounds that perform both functions are retinoids, especially retinol and all trans-retinoic acid.
Aged human skin can be benefitted by enhancing procollagen synthesis. We have found as another invention that procollagen levels can be increased in aged human skin by the preferably regular application to the skin of effective amounts of a retinoid; in preferred embodiments, the treatment also includes inhibition of collagen degradation by the use of an MMP inhibitor.
In addition to treating and/or preventing chronological aging of the skin, our discovery that effective amounts of a retinoid applied to the skin can increase procollagen synthesis provides another invention in the prevention (prophylaxis) of skin ulcers. By increasing the collagen content of the skin, the form, strength, and function of the skin is enhanced. Increased procollagen synthesis, and thus an increase in collagen content of the skin, mitigates the loss of strength and support due to reduced, degraded collagen, and so improved procollagen synthesis is expected to diminish the occurrence and/or severity of skin ulcers.
In connection with the foregoing, we have found as yet other inventions that keratinocytes and fibroblasts, each beneficial to the integrity of the skin, are each increased in number by the topical application of a retinoid, again applied preferably on a regular basis. Fibroblasts are trophic to the epidermis; under normal conditions they secrete a number of growth factors (e.g., FGF, IGF, and KGF, among others) and produce procollagen that enters the dermal matrix and become structural collagen.
Yet another invention is decreasing cJUN activity and/or reducing, the amount of c-Jun protein present in the skin, and increasing ERK activity, both in aged skin, by the topical application of an effective amount of a retinoid to the aged skin.
In additional embodiments, prophylaxis and treatment of dermal chronoaging are each enhanced by applying along with the active ingredient at least one additional compound selected from: a sunscreen for at least one of UVA1, UVA2, and UVB; an antioxidant; an MMP (matrix metalloproteinase) inhibitor; and mixtures thereof